1. Field of the Invention
The present invention relates to a method and apparatus for a mobile communication system. More particularly, the present invention relates to an improved power headroom report method and apparatus for a mobile communication system supporting carrier aggregation.
2. Description of the Related Art
Mobile communication systems have been developed to provide subscribers with voice communication services on the move. With the advancements of various technologies, the mobile communication systems have evolved to support high speed data communication services as well as the voice communication services.
Recently, as a next generation mobile communication system of the 3rd Generation Partnership Project (3GPP), Long Term Evolution (LTE) is under development. The LTE system is a technology for realizing high-speed packet-based communication at about 100 Mbps. Regarding the commercialization of the LTE system, a discussion is being held on several schemes, namely one scheme for reducing the number of nodes located in a communication path by simplifying a configuration of the network, and another scheme for maximally approximating wireless protocols to wireless channels.
Unlike voice communication service, data communication service is characterized in that the resource is allocated according to the amount of data to be transmitted and channel conditions. Accordingly, in the wireless communication system, such as cellular communication system, a scheduler manages resource allocation in consideration of the amount of resources, channel conditions, and amount of data. It is also the case in the LTE system that the scheduler, which is located in the base station, manages and allocates the radio resources.
Recently, LTE-Advanced (LTE-A) is actively being discussed as an evolution of the LTE with new techniques to increase the data rate. Carrier Aggregation (CA) is one of the representative techniques that are newly adopted in LTE-A. Unlike data communication of the related art in which a User Equipment (UE) uses a single uplink carrier and a single downlink carrier, the carrier aggregation enables the UE to use multiple uplink and/or downlink carriers. Since the uplink transmission power determination algorithm of the related art is designed for the UE operating with one uplink carrier and one downlink carrier, it is difficult to apply the transmission power determination process of the related art for uplink transmission power determination of the UE supporting carrier aggregation. In particular, there is a need to define a procedure and method for reporting Power Headroom (PH) of the UE supporting carrier aggregation.